How to know the types of windowing system, window manager and desktop environment of a Unix-like OS

From Ask Ubuntu.SE: If you have wmctrl installed, wmctrl -m will identify the window manager for you.

Thomas already mentioned the XDG_CURRENT_DESKTOP environment variable for identifying the desktop environment.

And from this thread here in Unix & Linux SE: the XDG_SESSION_TYPE environment variable can be used to identify whether the windowing system is X11 or Wayland.

One of the answers in the comments works for me in Kali (probably in other Debian-based distros as well)

env | grep XDG_CURRENT_DESKTOP

With difficulty.

There is no centralized system for keeping track of these things.

• On Debian-derived Linuxes you might try the alternatives system.
• You could query the package manager, and if you find only one Foo installed, you can be pretty sure which Foo is in use.
• You could try parsing the output of ps. Or equivalently of reading /proc on systems that have it.

Possibly the most reliable thing is to ask the user.